Delayed neurotoxicity induced by some organophosphorus compounds including tri-ocresyl phosphate (TOCP) is characterized by a delay period of 6 to 14 days before the onset of clinical signs after the administration of a single dose of a neurotoxicant. The clinical condition becomes manifested first as ataxia followed by paralysis. Some animal species are sensitive to organophosphorus-induced delayed neurotoxicity (OPIDN) such as chickens and cats while others such as rodents are not. OPIDN is also known to be age related since chicks and kittens are more tolerant than chickens and cat, respectively. This proposal is designed to study qualitatively and quantitatively the in vitro metabolism of the industrial neurotoxic [14C]TOCP by subcellular fractions from sensitive and insensitive animals. The subcellular fractions include the mitochondria, the microsomes and the soluble fractions which will be prepared from liver, kidney, brain, spinal cord and sciatic nerve from adult chickens as a sensitive species and from rats as insensitive species. Also these fractions will be prepared from kittens and chicks in order to study age related factor(s) involved in the sensitivity to OPIDN. The effect of the inducers phenobarbital and 3-methylcholanthrene on the metabolism of TOCP will be studied using rats and chickens. The metabolic systems involved in TOCP metablism will be characterized using various inhibitors and cofactors. High performance liquid chromatography (HPLC) and liquid scintillation counting will be used to identify and quantify various metabolites formed by various subcellular preparations. We have synthesized these metabolites of TOCP: di-o-cresyl hydrogen phosphate, o-cresyl dihydrogen phosphate, saligenin cyclic o-tolyl phosphate and hydroxy methyl TOCP and their structures were varified by IR, 1H NMR and mass spectroscopy. We also developed an analytical method utilizing HPLC to separate TOCP and various metabolites. This HPLC method was used successfully for the analysis of TOCP and its metabolites extracted from excreta and other tissues of cats treated with TOCP. This study is designed in order to study the relationship between metabolism and species and age sensitivity to delayed neurotoxicity induced by TOCP. It may shed some light on the mechanism by which OPIDN is produced and thus help us to understand more about how to protect humans from delayed neurotoxicity.